<html>
    <head>
        <title>My First Webpage</title>
        <style>
            h1 {
                background-color: #ff0000;
            }

            h1.app:hover{
                background-color: #00ff00;
            }
        </style>
    </head>
    <body>
        <h1 class="app">Hello World</h1>
        <p>This is my first webpage.</p>
    </body>
</html>